The present invention relates to a method for temporarily protecting a sticky surface of an adhesive sheet material having a layer of a silicone-based sticking agent and an adhesive sheet material thus protected from inadvertent sticking with a peelable protecting sheet or a release sheet.
A variety of adhesive sheet materials are currently used such as adhesive labels, adhesive tapes and the like. Such an adhesive sheet material is formed by providing a layer of a sticking agent on the surface of a substrate sheet material such as papers, plastic films, metal foils and the like according to particular needs and is conveniently used to be bonded with stickiness on to the surface of an article without the necessity of re-moistening with water as in postage stamps. Owing to the convenience in their use, demand for such adhesive sheet materials is rapidly growing.
One of the problems in the adhesive sheet material is the protection of the sticky surface from inadvertent sticking to an undesired surface. A generally practiced method is to bond a so-called peelable release paper to the sticky surface of the adhesive sheet material for temporary protection and the release paper is removed by peeling directly before use of the adhesive sheet material. Needless to say, the performance of temporary protection by use of a peelable release paper largely depends on the combination of the sticking agent forming the sticky layer on the surface of the adhesive sheet material and the releasing agent or anti-sticking agent to impart releasability to the surface of the peelable release paper. The requirements for the peelable release paper are diversified. For example, the release paper once bonded to the sticky surface must not spontaneously come off without an outer peeling force but it must be readily removed by peeling with a relatively small peeling force when desired causing no decrease in the sticking power of the adhesive sheet material or so-called residual sticking power.
The above mentioned requirements for the combination of the sticking agent and the releasing agent are sometimes contradictory to each other so that no single method of temporary protection hitherto proposed is applicable to all kinds of the adhesive or sticking agents. Various types of sticking agents are used in the art including natural rubber-based ones, acrylic ones, terpene-based ones and silicone-based ones. On the other hand, the releasing agents most widely used for the preparation of peelable release paper are those based on a silicone releasing agent by virtue of the outstandingly excellent performance in comparison with the releasing agents of the other types. Satisfactory temporary protection of the sticky surface is obtained with such a silicone-treated peelable release paper when the sticking agent in the sticky layer of the adhesive sheet material is not a silicone-based one.
Unfortunately, silicone-treated peelable release papers are relatively ineffective for the temporary protection of the sticky surface of the adhesive sheet materials having a surface layer formed with a silicone-based sticking agent. Therefore the application of the silicone-based sticking agents is unduly narrowly limited despite their very high performance as a sticking agent per se due to the lack of an effective means for temporarily protecting the sticky surface thereof on the adhesive sheet materials.